RUBBISH will be piling up in Hong Kong's streets by early next year if a controversial government scheme for charging landfill users is not implemented soon, a government official said.

For at present dumping rates, two of the territory's three established landfills will be exhausted before replacements are ready, said Nick Fry, an assistant secretary with the Planning, Environment and Lands Branch.

''If we haven't got the system in place by Chinese New Year, there is going to be big trouble,'' he said. That includes rubbish on the streets.

About 20,000 tonnes of garbage, roughly 60 per cent of which comes from building sites, are dumped each day at a new landfill in Tuen Mun, and three older sites at Tseung Kwan O, Sheung Wan and Pillar Point which are due to close by the end of next year.

Tseung Kwan O will probably last until early next year. Its replacement, the southeast New Territories landfill, is due to open next month, but heavy rain may delay this as well as reduce the capacity of the old site. Sheung Wan should last until spring, but its replacement in northeast New Territories is not due to open until July.

The plan to charge landfill users is an imperfect but urgently-required stopgap move to prevent Hong Kong running out of space, Mr Fry said.

Dumping is currently free. But the Government hopes the charges will extend the life of the two severely strained landfills by encouraging building firms to sort their waste and dump only degradable material such as paper and wood. Rubble and other inorganic material can currently be disposed of free at dumps in Tseung Kwan O and Aldrich Bay, where it is used for reclamation projects.

But Mr Fry admits the plan may have little effect if construction firms find the sorting costs too high.

Private waste collectors support landfill fees, but have branded the proposed scheme as ''archaic, arbitrary, discriminatory and illogical''.

The flat-rate charges - $175 for loads under five tonnes and $350 for those over five tonnes - fail to take into account the type and size of vehicles used to collect waste, said the Environmental Contractors Management Association (ECMA).

It wanted a computerised weighing system that would invoice companies for each tonne of trash.

The association, responsible for about 40 per cent of the privately collected non-construction waste dumped in landfills, also believed the Government's pre-paid ticket scheme would raise administrative costs, cause delays and could be abused by drivers.

''What happens if the truck carrying 5.1 tonnes is at the paybooth and the driver doesn't have enough tickets?'' ECMA vice-president Francis Tan Chong-wai said.

''This will cause traffic congestion. Drivers could also sell these 'quasi-money' tickets to other companies, so they are open to abuse.'' Mr Fry said the Government eventually hoped to use electronic weighing systems with payment by stored-value tickets.